"Spontaneous Spawnings:" Luck, coincidence...or something else entirely?

As a kid, I remember that the idea of breeding my fishes seemed so exotic; so aspirational...and often, unachievable.

Sometimes, it still feels that way, especially with some fishes.

I mean, sure, I was able to breed livebearers, killies, Kribs, Zebra Danios, Apistos, Cherry Barbs- fishes like that. Sometimes, these were the result of random chance, coincidences, or just plain old luck. Usually, my deliberately organized breeding attempts just sort of came up short all the time.

I mean, I'd have some success.

I had various Tetras breed when I intentionally tried to do it. However, for the most part, my "career" as a deliberate fish breeder has been essentially lacking. For whatever reason, I just don't have that combination of skill, desire, and a certain kind of patience that almost every talented fish breeder seems to possess in abundance.

The combination which leads to success with so many types of fishes.

And, that's okay. I made peace with that a long time ago.

My path as a hobbyist sort of took a different direction. And in the end, I've learned a lot more about the environments from which my fishes come, and ways to replicate various aspects of them in more compelling ways.

And along the way, I would end up with a surprisingly large number of those "spontaneous" spawning events with my fishes. You know, you wake up one morning and your Pencilfishes are acting weird...Next thing you know, there are clouds of eggs flying all over the tank...

That sort of stuff.

And after the initial surprise and excitement, during my "postgame analysis", I'd be trying to figure out what led to the spawning event...

And after a few years of experiencing this sort of thing, I began to draw the conclusion that it was the result of going out of my way to focus on recreating the correct environmental conditions for my fishes on a full-time basis- not just for spawning- which led to these events occurring repeatedly over the years.

With all sorts of fishes, too.

When it happened again, not too long a go, in my experimental leaf-litter only tank, hosting about 20 Paracheirodon simulans ("Green Neon Tetras"), I came the conclusion, in a circuitous sort of way, that I AM a fish breeder of sorts. Or, more precisely, a "fish natural habitat replication specialist." A nice way of saying that by focusing on the overall environmental conditions of the aquarium on a full time basis, I could encourage more natural behaviors- including spawning- among the fishes under my care.

Of course, there is more to being a "successful" breeder than just having the fishes spawn. You have to rear the resulting fry, right? Sure, half the battle is just getting the fishes to lay eggs in the first place- a conformation that you're doing something right to make them comfortable enough to want to reproduce! And there is a skill set needed to rear the fry, too.

Yet, I think that with a more intensive and creative approach, our botanical-style aquariums can help with that aspect too. Sure, it's more hands off than the traditional "keep-the-fry-knee-deep-in-food-at-all-times" approach that serious breeders employ...but my less deliberate, more "hands-off" approach can work. I've seen it happen many times in my "non-breeding" tanks.

And of course, it's not just me. I hear all the time from hobbyist who play with botanical-style aquariums about these sort of "spontaneous spawning" and the appearances of fry in their tanks..

t happened yet again...an excited email from a customer who recently switched over to a botanical-style, blackwater aquarium, only to have her little Boraras, which she'd had for over a year, suddenly start spawning!


Now sure, it could just have been that they finally were of spawning age, or that the temperature in her tank changed one night, or...and number of a dozen possible factors. However, I hear these stories from hobbyists fairly often.

Actually, all the time.

We're seeing more and more in botanical-stye, blackwater aquariums are reports of "spontaneous" spawnings of all sorts of different fishes associated with these types of conditions.

Often, it's a group of fishes that the aquarist had for a while, perhaps with little effort put into spawning them, and then it just sort of "happened." For others, it is perhaps expected- maybe the ultimate goal as it relates to a specific species...but was just taking a long time!

The "common denominator" in all of the reports we receive are that the fishes are displaying better overall color, vigor, and overall health after being recently exposed to the more "physiologically appropriate" conditions of a blackwater aquarium. Now, this is by no means us stating that blackwater/botanical-style tanks are somehow magical, and possess the ability to make every fish magically thrive and spawn- or that this is some amazing "secret" that we've stumbled upon.

Nope. It's as old as the hobby itself. It's hardly magic.

Rather, it's more of an affirmation of a theory which I've developed over the decades that fishes from specialized environments- even those which might be several generations captive-bred, can always benefit from being "re-patriated" to the conditions under which they have evolved for eons.

I know that there are those who will adamantly state that this is not necessary or true, and that they breed Discus just fine in hard, alkaline tap water, or whatever- but I just have this really hard time accepting the argument that fishes from say, soft, acidic blackwater are somehow "better off" in hard, alkaline "tap water" conniptions...after only a few dozen generations in captivity.

Have we somehow "changed" the physiology or physiological needs of the fish, which evolved over millions of years, in a few decades?

I'm not buying that argument! 

"Acclimated" to the water parameters that work for US? Sure...However, "changed" their physiological requirements for certain conditions?

Nah. Not buying that. 

Now, I could be totally wrong, but I'm not listening anyways...lol (I'm not irrationally stubborn or anything...LOL)

Look, this L.A. boy, who's lived all of his life in warm temps CAN adapt to living in frigid Antartica, if I'm given the proper clothes, housing, etc. I could even start a family there. Yet, does this mean that we've somehow evolved to thrive in these conditions?

No, I merely acclimated to it and figured out how to "deal" with it.

Of course, with botanical-style aquariums, we know that we have a few things going for us already.

I think there is a lot to be said for the potential benefits of humic substances for fishes- substances which are found in abundance in the natural botanical materials we play with-and indeed, much research has been done in this area already by science. Still, much is yet to be fully understood, but suffice it to say, there are a variety of health benefits ascribed to humic substances found in blackwater and other  habitats, and the "superficial", yet numerous observations we've made thus far seem to confirm this!

What advantages do they give us when we're trying to breed fishes from these habitats?

One could generally state that they reduce stress, if nothing else, right? That's at least a start. It's long been known that fishes kept under conditions which minimize stress are healthier overall, and part of the overall health is that they will engage more readily in natural behaviors such as spawning.

DO botanica-style aquariums accomplish this?

I think so. However, I'll be the first to admit that we're still learning about this stuff, aren't we? So to draw anything more than the most superficial conclusion is just speculative.

Now, as I touched on above, I am equally fascinated by the possible benefits of these conditions for fry. In other words, not only the chemical conditions (i.e; pH, levels of tannins/humic substances, etc.), but the possibility of providing natural foods and nutritional benefits from the biofilms which botanicals and leaves "recruit" while underwater.

We already know from studying Nature that biofilms will serve as an excellent natural source of food- supplemental or otherwise- for many fish fry.

Biofilms and the organisms which are found with them are consumed by a number of species as adults, so it goes without saying that, if they're available to fry, they might also be a possible source of nutrition.

Which leads me to wonder...

Could a botanically-"stocked" aquarium, complete with perhaps a deep leaf litter bed and/or lots of botanicals, "doing their thing", serve as a sort of "nursery" for fry of fishes which are adapted to blackwater conditions? Or any number of other environmental conditions, for that matter?

I think so!

I've talked about this many times before- including quite recently.

So, perhaps a version of the fry-rearing tank that's a bit more than the typical bare-bottomed, hyper-maintained nursery tanks we tend to use so often- might be a good thing to experiment with? I mean, sure, for commercial breeding, it probably would be a challenge...but for the hobbyist working with just a few species...could this be a great way to provide some supplemental/primary feeding? A sort of "botanical refugium" for fry? 

I think there is precedent.

I mean, what hobbyist hasn't had one of those planted "jungle" tanks over the years, where you'd just sort of "stumble" on well-developed, well-fed fry from time to time in the "canopy" of plants? I mean, same idea, right? Natural foods...and protection?

I think that we might see some of this as more and more hobbyists experiment with botanical-style brackish tanks, too! A lot of potential discoveries- even breakthroughs- are possible! 

None of this stuff is completely mind-blowingly revolutionary. But it is evolutionary...a sort of possible progression in thinking. It's not really "rocket science" ("Filll tank with water. Add leaves and let them decompose. Add fish fry.")

I'll say it again: Much research needs to be done. 

Meanwhile, I'll never tire of my seemingly "challenging" fishes "spontaneously" spawning in my botanical-style aquariums. And I'll continue to think about what may have led to these exciting events.

The fact is, I'm doing nothing differently than any other hobbyist who has ever bred fishes has done. The only different thing is that I am not providing these conditions for the expressed benefit of spawning the fishes. 

The fishes are simply doing what comes natural.

Maybe it's inevitable?

They're simply reacting to proper environment and nutritional parameters. If they had slightly different requirements, perhaps these spawnings would likely not have taken place. This happy result is simply the combination of selecting fishes carefully for the environment that was prepared for them and consistent husbandry.


Coincidence? Possibly. Luck? Perhaps.

Yeah, it's not "rocket science" by any stretch. It's the result of adhering- admittedly in a slightly different way- to the basic approach handed down to us by generations of hobbyists:

Give your fishes the best possible environmental conditions and food, and you're likely to have success spawning them.

Want to succeed with spawning fishes?

So why not make the "easy" part of the equation, well...easy, and at least focus on providing your fishes-even if they're just in a display- with the conditions they would need if you were attempting to spawn them intentionally? It's one of those "no-brainer" things in fish keeping that should be immediately obvious, but we tend to overlook in our busy, daily lives and the many other commitments besides our aquariums that fill them.

The results just might surprise you.

Then again, maybe they won't.

Stay diligent. Stay curious. Stay excited. Stay consistent.

And Stay Wet.


Scott Fellman

Tannin Aquatics



Scott Fellman
Scott Fellman


2 Responses

Scott Fellman
Scott Fellman

July 27, 2020

Hi Rene!

Glad to hear of your experiences with this approach! I think that we’re all looking for the best techniques to breed fishes…Like you, I just can’t help but wonder why we don’t do that on a full-time basis! Im happy that you’re sharing this experience and success! You’ve very nicely encapsulated the lessons from this for all to enjoy and understand- Thanks so much for sharing! -Scott

René Claus
René Claus

July 27, 2020

Hi Scott,

You make some very good points.

I am not a fish breeder but have been a fish keeper for 35/40 years now (oh my..;). From labyrinth fish to discus and angels to catfish and tetras, I’ve kept them all. And many, yes including the discus, have spawned in my ‘community’ tank.

I kept Bettas and Paradise fish when I was a kid and I learned very fast that when I let the tank grow a little wild, put some peat in the filter and maybe give the fish some live food when available, they started to build a foam nest in no time. ’The more natural, the better’ always seemed obvious. But I also remember reading in those days about breeding tetras for instance, there was always this view that the circumstances created for breeding were for breeding only and not for your ’normal’ tank. This was mainly about water chemistry and not so much about creating a natural environment but somehow it still puzzled me. You create a situation to make the fish feel super but then you only do that for a certain period…hmmm.

Of course, when you have a community tank with fish from different habitats you need to find a balance, certainly in water chemistry. But creating the most natural circumstances possible in your tank will always be beneficial to the health of your fish, always. Even for captive bred fish who have never seen the Amazon or the jungles of Borneo. I am 100% with you. If you keep fish from these habitats (soft, acidic jungle streams), decaying leaves and branches are a must have. Let it rot in the tank, really. It’s a natural food, for adult and young, it’s anti-bacterial and it improves water quality. However, make sure to have a good working filter and do regular water changes! That is a must.

I have a 2 metres South American community tank in my living room with tetras, cichlids and catfish. Sandy bottom and lot’s of branches collected from nearby forests. There are always leaves in the tank, palm leaves, almond leaves or self collected beach and oak. The water is brown. and the fish are happy. In other words, I couldn’t agree more with your blog!

Cheers from the Netherlands


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